1. Field of the Invention
The present invention relates to a method of hydrocracking heavy oils or extraheavy oils with the generation of coke being suppressed. More specifically, the present invention relates to a method of hydrocracking heavy oils or the like wherein the generation of coke is suppressed in the presence of pressurized hydrogen and a catalyst comprising active carbon having specific properties and comprising iron carried on the active carbon, and heavy metals such as Ni and V, asphaltene, residual carbon, sulfur, nitrogen and the like in the heavy oil or extraheavy oil, are removed by cracking and subjected to a heat treatment.
2. Description of the Related Art
Recently, as the world-wide trend in the petroleum refinery industry, the proportion in production of light-weight products is increasing. Accordingly, it is becoming more and more important, from the standpoint of effective utilization of resources, that heavy oils or extraheavy oils such as atmospheric distillation-residual oils, vacuum distillation-residual oils, catalytically cracked residual oils, oil sand oils and coal-liquefied oils and the like, which remain after removing valuable light-weight fractions, can be hydrocracked and further converted into useful intermediate fractions.
There have been a number of reports about the hydrocracking of heavy oils by using catalysts. As one example of upgrading heavy oils by using catalysts containing active carbon having specific properties with a metal carried thereon, U.S. Pat. No. 5,358,634 and U.S. Pat. No. 5,364,524 have been proposed.
In U.S. Pat. No. 5,358,634, a process of hydrocracking heavy hydrocarbon oils by using an active carbon catalyst having specific properties is disclosed. This is a method of cracking a heavy hydrocarbon oil which contains no less than 70% of a heavy oil content having a boiling point of not lower than 343xc2x0 C. in a fixed-bed reactor. The reference suggests that, according to the method, under the existence of active carbon having at least 0.2 cc/g of pore volume and at least 50 m2/g of surface area of a pore distribution range of 10-40 nanometers, the average pore diameter being 4 to 5.4 nanometers, the heavy metal (Ni and V) removal rate is at least 59%, the desulfurization rate is at least 9.5%, the residual carbon decomposition rate is at least 13.5% and the removal rate of asphaltene defined as a content insoluble to pentane is at least 10%.
U.S. Pat. No. 5,364,524 discloses a process of hydrocracking a heavier oil. This is a method of hydrocracking a heavy hydrocarbon oil which contains no less than 97% of a heavy oil content having a boiling point of not lower than 343xc2x0 C. in a fixed-bed reactor. The reference suggests that, according to the method, under the existence of a catalyst in which Mo (or W) and Co (or Ni) are carried on an active carbon carrier having properties including at least 0.2 cc/g of pore volume and at least 50 m2/g of surface has a pore distribution range of 10-40 nanometers, the average pore diameter being 4 to 6 nanometers, at least 23% of Ni and V can be removed.
These prior arts are clearly different from the present invention which will be described below, in terms of the properties of the catalyst, the types of metals carried on the catalyst, the type of the reactor, as well as the heavy metal removal rate and the residual carbon decomposition rate.
On the other hand, the applicant of the present invention has proposed in JP-A 6-165935 a method in which hydrocracking with a relatively small amount of hydrogen consumption is made possible by using, as the hydrocracking catalyst for heavy oils, a catalyst in which metal active components such as nickel and iron selected from group VIII in the periodic table are carried on active carbon produced from brown coal as a carrier. However, according to this method, as heavy oils are hydrocracked at only one stage in the process, it is difficult to reduce the amount to be used of the catalyst and suppress the generation of coke at a high conversion rate.
In addition, the applicant of the present invention has proposed in JP-A 9-235569 a method of hydrogenating heavy oils at two stages as one of the improved versions of the technique belonging to catalytic hydrocracking. In order to carry out the hydrocracking of heavy oils in two stages, this method comprises: a first step of adsorbing a coke precursor and coke into a coke adsorbent to remove them, the coke precursor and the coke being obtained by carrying out a thermal decomposition of the heavy oil under the existence of 2 to 10 wt. % of the coke adsorbent to the feedstock oil and hydrogen; and a second step of carrying out a thermal decomposition of the substantially whole amount of the thermally decomposed oil obtained by the first step from which the coke precursor and the coke have been removed, under the presence of hydrogen, iron compounds and active carbon having properties such as a MCH conversion rate of 45-85%, specific surface area of 800-1000 m2/g, pore volume of 0.7 to 1.4 cm3/g, mesopore (2-50 nanometers) volume of not less than 70% and average pore diameter of 3-6 nanometers. The coke adsorbent of the first step comprises: at least one carbon material selected from the group consisting of brown coal, brown coal char, petroleum cokes, active carbon, carbon black and graphite; and at least one member of iron compounds selected from the group consisting of iron sulfide, iron oxide and natural pyrite. At the first step, the carbon material and the iron compounds are present in a simply mixed state in the heavy oil. The iron compound of the second step includes at least one member of compounds selected from the group consisting of iron sulfide, iron oxide and natural pyrite. At the second step, the active carbon and the iron compounds in the thermally decomposed oil are present in a simply mixed state. However, in the method of simply mixing the carbon material and the iron compounds in the hydrogenation of heavy oils at two stages as disclosed in JP-A 9-235569, since the density of the carbon material and that of the iron compound differ from each other and, as the reaction proceeds, each density varies according to the amount of coke precipitated and heavy metals deposited on the carbon material and the iron compound, selection of the conditions in fluidization operation using gases and liquids for homogeneously dispersing the catalyst becomes complicated and difficult.
In the method in which the carbon material and the iron compounds are present in heavy oils in a simply mixed state, if the conditions in fluidization operation are selected such that the catalysts are homogeneously dispersed in the reactor, a suspension type or slurry bed may be selected and the catalysts flow out of the reactor with gases and cracked oils. In a case in which there is a preposition that catalysts are disposed of after use, such a suspension type may not be a problem. However, if re-use of the catalysts which still keeps a sufficient level of activity is intended, it is necessary to separate the catalysts which have flowed out of the reactor from the cracked oils and to recycle the separated catalysts to the reactor, which makes the process complicated.
In the RFCC processes for increasing production of the gasoline fraction and the process of hydrodesulfurizing feedstock to be supplied to the RFCC processes, when a feedstock which contains a relatively high amount of residual carbon content and metals such as Ni and V is supplied, some of the residual carbon and metals poison the catalyst and deterioration of the catalysts occurs, although the degree of the deterioration depends on the feedstock to be supplied. Conventionally, in hydrodesulfurizing, a step of removing Ni and V, in what is called a guard reactor, is provided prior to the hydrodesulfurization in order to reduce deterioration of the catalysts due to deposition of Ni and V and precipitation of coke on the catalysts. In the case of the catalyst used here, the pores of the alumina carrier are made larger so that a relatively large molecule of asphaltene, which contains Ni and V, be decomposed and thus Ni and V be removed. However, the catalytic ability is not sufficient and complicated operations including frequent switching of the reactor, constant supply/removal of the catalysts and the like are frequently necessitated, in order to replace the catalysts which have been deactivated due to precipitated coke and deteriorated due to deposition of Ni and V thereon.
Lillian A. Rankel, Energy and Fuels 1993, 7, 937-942 discloses properties of a catalyst containing active carbon with metals carried thereon, i.e., a CoMo/carbon catalyst, whose properties are shown in Referential Example 1 described hereinafter. In this catalyst, the V removal rate is equal as compared with the catalyst of the present invention, but the conversion rate is suppressed at a low level in order to prevent generation of coke. In addition, the Ni removal rate, the desulfurization rate and the residual carbon removal rate thereof are also suppressed at a relatively low level. Accordingly, it is obvious that the performances of the catalyst of the present invention are more excellent than those of the aforementioned catalyst.
Further, it is difficult to process used alumina catalysts on which Ni and V have been accumulated. Expecting that, in the future, crude oil will probably become heavier, that is, contain more heavy metals, more residual carbon and the like, when materials containing more heavy metals, asphaltene and residual carbon, etc. will be supplied under such a circumstance, it has been desired that a technique which enables, with a high efficiency, removal of heavy metals from the feedstock and decomposition of asphaltene, residual carbon etc. in the aforementioned process is developed.
In short, excellent techniques for processing extraheavy oils which contain a significantly large amount of impurities, such as heavy metals (Ni and V), asphaltene and residual carbon, will become essential in future.
Catalysts can be used in a fixed-bed. However, when extraheavy oils are processed, especially, since heavy metals like Ni and V as impurities contained at a high percentage in the extraheavy oils are more likely to deposit on the catalysts and cokes generated from asphaltene and residual carbon are more likely to precipitate, it is very important that the catalysts are homogeneously dispersed in the reactor and the fluid state thereof is sufficiently maintained so that the reaction temperature be evenly maintained and partial retention of the deposits and precipitates be prevented.
The object of the present invention is to propose means for solving all of the aforementioned problems at the same time.
The inventors of the present invention have, as a result of assiduous study for solving the problems of the prior art, discovered that, by using a catalyst in which iron is carried on active carbon, the catalyst can be effectively used until the catalyst loses its activity without allowing the catalyst to flow out of the reactor and the reaction temperature can be evenly maintained and partial retention of the deposits and precipitates can be prevented because conditions in fluidization operation by gases and liquids can be easily selected and homogeneous dispersion of the catalyst and a fluid state can be sufficiently maintained, thereby allowing the catalyst to demonstrate its full capacity as a catalyst in achieving suppression of coke-generation and removing heavy metals. The invention has been completed on the basis of these discoveries.
That is, the present invention discloses a catalyst for the hydrocracking of heavy oils, comprising iron and active carbon having properties of an MCH conversion rate of 40-80%, a specific surface area of 600-1000 m2/g, a pore volume of 0.5 to 1.4 cm3/g, a 2-50 nanometers"" mesopore volume of not less than 60% and an average pore diameter of 3-6 nanometers, the iron being carried on the active carbon in an amount of 1-20 wt. % with respect to the active carbon.
In addition, the present invention discloses a method of hydrocracking heavy oils and the like by using the aforementioned catalyst, which comprises the first step of conducting hydrocracking at a temperature within the range of 360-450xc2x0 C. at a hydrogen partial pressure of 2-14 MPaG and the second step of conducting hydrocracking at a temperature within the range of 400-480xc2x0 C. at a hydrogen partial pressure of 2-18 MPaG.
Further, the present invention discloses a method of hydrocracking the heavy oils and the like, wherein in the first and second steps, the concentration of the catalyst is 6-40 wt. % of the oil or oil having been treated by heating.
Also, use of the catalyst to hydrocrack heavy oils is provided.
The present invention exhibits excellent effects in hydrocracking of heavy oils, and especially exhibits distinguished effects in hydrocracking of extraheavy oils.
Heavy oils and the like include heavy oils and extraheavy oils, or oil sand oils, oil shale oils, coal-liquefied oils and the like. The heavy oils and extraheavy oils are residual oils, such as atmospheric distillation residual oils, vacuum-distillation residual oils and catalytically cracked residual oils, derived from crude oil or petroleum. As the heavy oils, Middle-Eastern based Arabian heavy, Basra, Kafdi, Iranian heavy and the like are used. As the extraheavy oils, Maya produced in Mexico, Athabasca oil sand bitumen and Cold Lake oil sand bitumen produced in Canada, Orinoco tar, Cerro Negro, Zuata, Bachaquero and Boskan produced in Venezuela, Marlim produced in Brazil and the like are used.
As a material of the active carbon having specific properties of the present invention, brown coal is used. Examples of brown coals include Yallourn coal, Morwell coal whose ash content has been reduced to less than 3 wt. % and the like.